1. Field of the Invention
The present invention relates to an image forming apparatus and a method of controlling the same.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2001-302003 discloses an image forming apparatus having a plurality of stacking unit. This reference discloses a method of, when sheets run out while executing image formation processing using sheets stacked on a given stacking unit, continuing the image formation processing using sheets stacked on another stacking unit.
However, the conventional technique suffers the following problem. Assume that image formation processing is in progress using sheets stacked on a given stacking unit. At this time, even if the user supplies sheets on another stacking unit and wants to continue the image formation processing using the sheets supplied by him, the stacking unit used in the ongoing image formation processing is kept used.